]> RIPE NCC

ondrej.caletka@ripe.net

Google, LLC

furry13@gmail.com

Operations and Management IPv6 Operations ipv6 nd vrrp ra This document provides operational guidance for configuring first-hop routers and first-hop redundancy in IPv6 networks. It also discusses design choices for improving recovery time after a renumbering event. About This Document Status information for this document may be found at . Discussion of this document takes place on the IPv6 Operations Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction Unlike IPv4, the IPv6 protocol supports operation with multiple gateways as a native part of the Neigbor Discovery Protocol . On the other hand, first hop redundancy protocols used in IPv4 like Virtual Router Redundancy Protocol can be used for IPv6 as well, making the redundant gateways appear as a single logical gateway. This document discusses different options for deploying redundant first-hop IPv6 gateways to ensure high availability and compatibility with various client implementations. First-hop routers face hosts and provide them with information to configure routing as well as well other network parameters, including but not limited to stateless address autoconfiguration, SLAAC .

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Design Choices to Provide First Hop Redundancy

Two (or more) independent Routers One of the posisble deployment scenarios is to deploy multiple routers in the same link. A host can choose one of those routers as a default router and if the selected router becomes unreachable, switch to another reachable one. If multiple routers are present on a link, Section 6.3.4 of requiresthat an IPv6 host MUST retain at least two router addresses and SHOULD retain more. If the administrator requires all hosts to use the same router, the following mechanisms can be utilized:

• Configure the default router preference .
• Advertize backup routers with Router Lifetime set to zero, changing that value to non-zero automatically when a primary router fails. This approach is similar to one described in .

The main disadvantace of this approach is time to recover: a host would only switch to another default router from the list after the Nighbor Unreachability Detection (NUD, ) marks the router as unreachable. The default value would be (without taking randomisation factors into account): ReachableTime milliseconds (to move from REACHABLE to STALE) + DELAY_FIRST_PROBE_TIME + MAX_UNICAST_SOLICITRetransTimer = 30 seconds + 5 second + 31 = 38 seconds. Since those timers timers are protocol constant (see Section 10 of or vary from one host operating system ti another, it is not possible to influence them from the network side. It is namely not possible to achieve shorter failover time by shortening the Router Lifetime of the active router to a very low value. Not only that leads to frequent sending of Router Advertisements, which has an impact on battery-powered devices , some operating systems are known to ignore routers announced with a very short lifetime.

Virtual Router Redundancy Protocol (VRRP) or Similar Protocols VRRPv3 specifies an election protocol that dynamically assigns responsibility for a Virtual Router to one of the VRRP Routers on a LAN. A Virtual Router has one or more dedicated virtual IPv6 addresses and a virtual MAC address. Hosts are provided with the virtual IPv6 address as the default router via Router Advertisements. Since the hosts only see a single high available logical gateway, the solution is also useful for hosts with broken IPv6 stacks which cannot correctly process Router Advertisements from multiple independent routers. Section 1.4 of compares convergence time between NUD (as discussed in the section above) and VRRPv3. Using VRRPv3 default parameters, a backup router can take over a failed default router in three seconds, with the switchover being transparent to hosts.

Anycast Default Gateway An Anycast Default Gateway assigns the identical IPv6 address and Virtual MAC (VMAC) address across multiple first-hop routers attached to the same broadcast domain or overlay network (e.g., EVPN-VXLAN). Similarly to the previous solution, hosts will configure a single high available logical gateway using Router Advertisements. Because every participating router concurrently processes and forwards first-hop ingress traffic, this approach provides active-active first-hop redundancy and multi-path forwarding. In the event of a router failure, convergence is dictated solely by local physical link-down detection or underlying L2/L3 topology reconvergence.

Routing return traffic back to Hosts All redundant gateways must correctly forward packets destined to the subnet where the hosts are connected, usually by means of an Internal Gateway Protocol (IGP). By default, this can lead to a routing asymmetry where return traffic uses a different gateway than the forward traffic. This is not a problem, unless some stateful processing like firewall rules or connection tracking takes place on the gateways. If routing asymmetry is not desirable and gateways are operated in active-standby mode, symmetric routing can be achieved by influencing the route metric of the active gateway announced in the IGP together with virtual IP/MAC address failover so that the currently active gateway will provide a more preferred route for the return path.

Timers Questions:

• How often to send RAs?
• How other times in RA should be re: to default router lifetime?

Host Mobility and Renumbering Evens AI: copy some text from draft-link-6man-gulla

Security Considerations This document does not introduce any new security considerations. It inherits security considerations of IPv6 (see ).

IANA Considerations This document has no IANA actions.

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document describes an optional extension to Router Advertisement messages for communicating default router preferences and more-specific routes from routers to hosts. This improves the ability of hosts to pick an appropriate router, especially when the host is multi-homed and the routers are on different links. The preference values and specific routes advertised to hosts require administrative configuration; they are not automatically derived from routing tables. [STANDARDS-TRACK] This document specifies the Neighbor Discovery protocol for IP Version 6. IPv6 nodes on the same link use Neighbor Discovery to discover each other's presence, to determine each other's link-layer addresses, to find routers, and to maintain reachability information about the paths to active neighbors. [STANDARDS-TRACK] RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document defines version 3 of the Virtual Router Redundancy Protocol (VRRP) for IPv4 and IPv6. It obsoletes RFC 5798, which previously specified VRRP (version 3). RFC 5798 obsoleted RFC 3768, which specified VRRP (version 2) for IPv4. VRRP specifies an election protocol that dynamically assigns responsibility for a Virtual Router to one of the VRRP Routers on a LAN. The VRRP Router controlling the IPv4 or IPv6 address(es) associated with a Virtual Router is called the Active Router, and it forwards packets routed to these IPv4 or IPv6 addresses. Active Routers are configured with virtual IPv4 or IPv6 addresses, and Backup Routers infer the address family of the virtual addresses being advertised based on the IP protocol version. Within a VRRP Router, the Virtual Routers in each of the IPv4 and IPv6 address families are independent of one another and always treated as separate Virtual Router instances. The election process provides dynamic failover in the forwarding responsibility should the Active Router become unavailable. For IPv4, the advantage gained from using VRRP is a higher-availability default path without requiring configuration of dynamic routing or router discovery protocols on every end-host. For IPv6, the advantage gained from using VRRP for IPv6 is a quicker switchover to Backup Routers than can be obtained with standard IPv6 Neighbor Discovery mechanisms. Informative References This document specifies the steps a host takes in deciding how to autoconfigure its interfaces in IP version 6. The autoconfiguration process includes generating a link-local address, generating global addresses via stateless address autoconfiguration, and the Duplicate Address Detection procedure to verify the uniqueness of the addresses on a link. [STANDARDS-TRACK] Frequent Router Advertisement messages can severely impact host power consumption. This document recommends operational practices to avoid such impact. This document discusses the most common scenarios of connecting an enterprise network to multiple ISPs using an address space assigned by an ISP and how the approach proposed in "Enterprise Multihoming using Provider-Assigned Addresses without Network Prefix Translation: Requirements and Solution" could be applied in those scenarios. The problem of enterprise multihoming without address translation of any form has not been solved yet as it requires both the network to select the correct egress ISP based on the packet source address and hosts to select the correct source address based on the desired egress ISP for that traffic. The aforementioned document proposes a solution to this problem by introducing a new routing functionality (Source Address Dependent Routing) to solve the uplink selection issue. It also proposes using Router Advertisements to influence the host source address selection. It focuses on solving the general problem and covering various complex use cases, and this document adopts its proposed approach to provide a solution for a limited number of common use cases. In particular, the focus of this document is on scenarios in which an enterprise network has two Internet uplinks used either in primary/backup mode or simultaneously and hosts in that network might not yet properly support multihoming as described in RFC 8028. Knowledge and experience on how to operate IPv4 networks securely is available, whether the operator is an Internet Service Provider (ISP) or an enterprise internal network. However, IPv6 presents some new security challenges. RFC 4942 describes security issues in the protocol, but network managers also need a more practical, operations-minded document to enumerate advantages and/or disadvantages of certain choices. This document analyzes the operational security issues associated with several types of networks and proposes technical and procedural mitigation techniques. This document is only applicable to managed networks, such as enterprise networks, service provider networks, or managed residential networks.

Acknowledgments TODO acknowledge.